The present invention generally relates to a fuel delivery system for an automotive vehicle.
Stringent emission standards for internal combustion engines suggest the use of advanced fuel metering techniques that provide extremely small fuel droplets. The fine atomization of the fuel not only improves emission quality of the exhaust, but also improves the cold start capabilities, fuel consumption and performance. Typically, optimization of the droplet size is dependant upon the pressure of the fuel, and requires high pressure delivery at roughly 7-10 MPa. However, higher fuel delivery pressure causes greater dissipation of the fuel within the cylinder, and propagates the fuel further outward away from the injector nozzle. This propagation makes it more likely that the fuel spray will condense on the walls of the cylinder and the top surface of the piston, which decreases the efficiency of the combustion and increases emissions.
Additionally, high pressure fuel systems typically require two fuel pumps. One low pressure pump within the gas tank, and one high pressure pump, which is driven by the camshaft of the engine and pumps the fuel at high pressure to the fuel rail. Upon starting, the engine is running slow, therefore, the high pressure pump which is driven by the camshaft of the engine takes a relatively long time to create the high pressures required by the system. At high engine speeds, the engine cannot use all of the fuel that the pump supplies, therefore, excessive fuel is bled back into the gas tank from the fuel rail. Further, most high pressure fuel pumps are piston pumps. Piston pumps have the distinct characteristic of delivering the fuel in pulses, whereby there is a surge of high pressure when the piston is pumping, and a lower pressure lag during the piston return stroke. Rotary pumps do not exhibit this pulsing behavior, however, rotary pumps are not capable of producing the high pressures that are required by a high pressure fuel delivery system. Therefore, there is a need in the industry for improvements upon existing fuel delivery systems, specifically, there is a need for a fuel delivery system which will deliver fuel to the cylinders of an automotive engine with a fine droplet size without requiring a high pressure auxiliary fuel pump.